The 198th prohibition is that we are forbidden from eating anything with chometz [leaven] mixed into it, even if it is not bread; e.g., muryas,1 kutach,2 etc.
The source of this commandment is G‑d's statement,3 "Do not eat anything leavened."
The Mechilta says, "The verse, 'Do not eat anything leavened,' comes to prohibit kutach from Babylon, beer from Medea, and vinegar from Edom. One might think that the punishment for eating them is kores; therefore the Torah says [in the verse which speaks of kores], 'chometz' — [one receives kores] only for that which is completely chometz, not for that which only has chometz mixed in. Why, then, are they mentioned at all? To teach us that one transgresses a negative commandment [by eating them]."4
It is explained in Pesachim5 that although one is forbidden from eating [anything with chometz mixed in], one does not receive lashes unless the mixture contained at least a k'zayis of chometz bich'dei achilas pras.6 If there was less chometz than this mixed in, one does not receive lashes for eating the mixture.
